A technique, in which two display panels overlap each other and an image is displayed on each display panel based on an input video signal, is conventionally proposed to improve contrast of a liquid crystal display device (for example, see Unexamined Japanese Patent Publication No. 2007-310161). Specifically, for example, a color image is displayed on a front-side (observer side) display panel in two display panels disposed back and forth, and a monochrome image is displayed on a rear-side (backlight side) display panel. Thus, contrast is improved. In the liquid crystal display device, adjustment is performed such that a whole gamma value of both the display panels becomes 2.2.